Solved

A question about if statements in VHDL

Posted on 2010-09-11
2
680 Views
Last Modified: 2013-11-13
Hey,

        I had a quick question about IF statements in VHDL, for some reason I keep getting this error:

ERROR:HDLParsers:164 - "C:/Xilinx/Workspace/Homework3/homework3.vhd" Line 23. parse error, unexpected IF

I have tried everything I could think of, and looked a little through google, but I can't figure out why it doesn't like the IF statement.

Appreciate any help on this.
library IEEE;
use IEEE.STD_LOGIC_1164.ALL;
use IEEE.STD_LOGIC_ARITH.ALL;
use IEEE.STD_LOGIC_UNSIGNED.ALL;

---- Uncomment the following library declaration if instantiating
---- any Xilinx primitives in this code.
--library UNISIM;
--use UNISIM.VComponents.all;

entity homework3 is
    Port ( num1 : in  STD_LOGIC_VECTOR(1 downto 0);
           num2 : in  STD_LOGIC_VECTOR(1 downto 0);
           result : out  STD_LOGIC_VECTOR(3 downto 0));
end homework3;

architecture Behavioral of homework3 is

begin
	--process (num1, num2)
	--begin
	if( (num1 = "00") or (num2 = "00") ) then
		result <= "0000";
	else if( (num1 = "01") and (num2 = "01") ) then
		result <= "0001";
	else if( (num1 = "01") and (num2 = "10") ) then
		result <= "0010";
	else if( (num1 = "10") and (num2 = "01") ) then
		result <= "0010";
	else if( (num1 = "01") and (num2 = "11") ) then
		result <= "0011";
	else if( (num1 = "11") and (num2 = "01") ) then
		result <= "0011";
	else if( (num1 = "10") and (num2 = "11") ) then
		result <= "0110";
	else if( (num1 = "11") and (num2 = "10") ) then
		result <= "0110";
	else if( (num1 = "10") and (num2 = "10") ) then
		result <= "0100";
	else
		result <= "1001";
	end if;
	--end process;

end Behavioral;

Open in new window

0
Comment
Question by:errang
2 Comments
 
LVL 5

Accepted Solution

by:
Kendor earned 500 total points
ID: 33656476
everytime you open up an "if" you have to end it with "end if;"

so basically what you are looking for is "elsif"

if .... then
elsif ... then
else
end if;

that should work :)
(make sure you reenable the process  - you have uncommented it now)

a side note on better code:
try to have a look at the "case" statement when using the process or the "select ... when" statement if you want to do it without
for your case you could for example do the following:

process....
variable temp: std_logic_vector(3 downto 0);
...
begin
...

temp := num1 & num2; -- here you concatenate the two inputs you can then use them in case:

case temp is
  when "00--" | "--00" => result <= "0000"; --- this does not work with all fpgas or synthesis tools. if after the case...
  when "0101"      => result <= "0001";
  when "0110" | "1001" => result <= "0010";
  when "0111" | "1101" => result <= "0011";
  when "1011" | "1110" => result <= "0110";
  when "1010" => result <= "0100";
  when others => result <= "1001";
end case;


end process;



or the select when would the look like

with num1&num2 select
  result <= "0100" when "1010" ,
                   ...,
                 "1001 when others;
0
 

Author Closing Comment

by:errang
ID: 33658900
Ah, awesome.

Been programming java so long didn't occur to me as what was wrong with it.. lol.
0

Featured Post

Free Tool: Subnet Calculator

The subnet calculator helps you design networks by taking an IP address and network mask and returning information such as network, broadcast address, and host range.

One of a set of tools we're offering as a way of saying thank you for being a part of the community.

Question has a verified solution.

If you are experiencing a similar issue, please ask a related question

A short article about a problem I had getting the GPS LocationListener working.
This is an explanation of a simple data model to help parse a JSON feed
The goal of the video will be to teach the user the difference and consequence of passing data by value vs passing data by reference in C++. An example of passing data by value as well as an example of passing data by reference will be be given. Bot…
The viewer will learn how to pass data into a function in C++. This is one step further in using functions. Instead of only printing text onto the console, the function will be able to perform calculations with argumentents given by the user.

831 members asked questions and received personalized solutions in the past 7 days.

Join the community of 500,000 technology professionals and ask your questions.

Join & Ask a Question